Typical endoscopes or manipulators, composed of an elongated insertion section that is inserted into a subject and an operating unit that is connected to a basal end side of the insertion section, have a bending section at a distal end portion of the insertion section so that the orientation of the distal end can be changed by bending the bending section. Mechanisms for bending the bending section include pulling a basal end portion of a wire connected to the bending section by manually turning a knob provided on the operating unit. Nowadays, the study of technologies for motorizing this bending mechanism is in progress, and technologies for replacing the current manual knob operation with motor driving are being actively studied (e.g., refer to Patent Literatures PTL 1 and PTL 2 below). For typical motor driving, the curvature angle of the bending section can be changed by an amount of curvature corresponding to the amount of operation as a result of the motor being rotated by an amount proportional to the amount of operation applied to the operating unit.
In practice, however, it is difficult to completely transmit the amount of pulling applied to the basal end portion of the wire to the distal end of the wire due to, for example, friction between the wire and members therearound and slackness of the wire. In other words, a nonlinear relationship holds between the amount of wire pulling and the amount of curvature of the bending section. Furthermore, this nonlinearity varies depending on the curved shape of the insertion section. Therefore, it is not possible to achieve superior and constant responsiveness in bending motion of the bending section to an operator's operation merely by making the amount of motor rotation proportional to the amount of operation. It is well known that such a decrease and variation in responsiveness also take place during advancement/retraction motion and rotational motion of a treatment tool disposed in a channel of the insertion section (e.g., see Patent Literature PTL 3 below).
To overcome this, an attempt is made in Patent Literatures PTL 1 through PTL 3 to improve responsiveness by controlling the motor so as to compensate for a decrease or variation in responsiveness in motion of the bending section or the treatment tool on the basis of the curved shape of a flexible section or the bending section. The motion of the treatment tool and the bending section is affected by the curved shapes of both the flexible section and the bending section. In PTL 1 through PTL 3, the curved shape of only one of the flexible section and the bending section is taken into account.